1. Field of Invention
The present invention relates to self-contained inertial navigation systems (INS) for interactive control using movable controllers in applications like computer display games.
2. Related Art
The Nintendo Wii Remote™ wireless controller is an example of the most recent state of the art advances in user interactive controllers for computer display game systems. It is a movable wireless remote controller, which is hand-held by the interactive user, that transmits input data to the computer controlled game display system via conventional short range wireless RF transmissions e.g., a Bluetooth™ system, and receives data via infra-red light sensors. This game controller is described in detail in Published U.S. Application US2007/0060384, (Mar. 15, 2007).
With movable controllers for game systems like the Nintendo Wii, it is desirable to use a self-contained INS system to sense and track the relative linear and angular motion of the movable controller. Current state of the art movable controllers do not have this ability. For example, the Wii Remote can use data it receives via its infra-red light sensors to infer information about its position and orientation from a set of external infra-red light sources that have been placed in the environment in some known configuration. But the use of light sensors means that the device depends on the light sources and is not, therefore, self-contained. The use of external signal sources is burdensome because the user must set up and configure those external sources. Furthermore, the user must restrict movements made with the controller so as to keep those external sources in view. A self-contained system has no such restriction on movement and requires no setup or configuration of external sources by the user.
Self-contained INS systems typically use sensors like accelerometers and gyroscopes. State of the art movable controllers like the Wii Remote use a tri-axial accelerometer. However, a single tri-axial accelerometer is insufficient to calculate all six degrees of freedom required to infer the linear and angular motion of a movable controller. In fact, it is impossible to even determine whether the controller is being translated or rotated, since a fixed rotation and a linear acceleration could generate the same set of readings on a single tri-axial accelerometer. However, by making assumptions on how the controller is held and along which axis it will be moved, it is sometimes possible to track the relative linear and angular motion. For example, in state of the art games for the Nintendo Wii, players are instructed on how to hold and move their controller. By assuming the players are approximately following the instructions, it is possible to interpret the signal from the tri-axial accelerometer to roughly track the relative linear and angular motion of the controller. But there is a wide class of games and other applications where it is undesirable to constrain how the user may move or hold the movable controller. State of the art movable controllers are therefore unnecessarily limiting.
To review the background of sensing the positions and tracking the paths of objects moving through three dimensional space, the tracking is done by inertial navigation systems (INS) which use a combination of accelerometers and gyroscopes to create or compute an inertial frame within which accelerations represent strictly linear acceleration in the world frame. If one knows the world frame linear acceleration of an object over time, one can calculate the current position of that object over time with respect to its starting location. If one knows the angular velocities of an object over time, one can provide its orientation at any point in time. Conventionally, in the tracking of objects, linear accelerations combined with angular velocities are necessary and sufficient for providing the location and orientation of an object with respect to a starting location. There are six unknowns that must be solved for at every point in time. Most INS (inertial navigation systems) use gyroscopes to fix or solve for the three angular velocities. Once the orientation over time is known, accelerometers can be used to track the three linear accelerations as described above. Reference is made to the publication, Radar, Sonar, Navigation & Avionics Strapdown Inertial Navigation Technology, 2nd Edition, D. Titterton and J. Weston, published in 2005 as part of the IEE Radar, Sonar, Navigation and Avionics Series, for an introduction to and further information on the field of inertial navigation systems.
Reference is also made to the publication, Design and Error Analysis of Accelerometer-Based Inertial Navigation Systems, Chin-Woo Tan et al., Published in June, 2002 by the University of California at Berkeley for the State of California PATH Transit and Highway System which is hereby incorporated by reference. This is a study of the feasibility of inertial navigation systems that use only accelerometers to compute the linear and angular motions of a rigid body. This publication relates to systems for measuring linear and angular velocities of motor vehicles and the like. Its determinations track motion on scale of tens of meters accuracy on a time scale of tens of minutes.